In my co-pending U.S. patent application Ser. No. 07/801,881, now U.S. Pat. No. 5,161,588 I have laid out the case for light-weight felling heads and disclosed a design for such a head. I also stated that such heads will permit smaller, lighter carriers. The level to which carrier weight can be reduced largely depends--in the case where the head is attached to the carrier by an extendible and retractable boom--on the maximum reach of the boom to be used, the maximum tree load that must be managed at that reach, and the type of terrain on which the machine is positioned. In the case where the felling head is directly connected to the carrier by a fixed length boom or forks, the carrier weight depends largely on the maximum tree load that must be managed, on whether each tree will be dropped to the ground as it is cut or whether one or more trees must be transported--in an essentially vertical position--and dumped in concentrations and, in the latter case, the type of terrain to be negotiated.
This invention relates mainly to the latter case where a carrier must travel over uneven terrain with a tree or trees in an essentially vertical attitude. The loads with which the carrier must cope are the direct weight of the tree or trees. This seldom exceeds the weight of the felling head and is therefore not a major factor in carrier stability considerations. The location of the centre of gravity of the tree load, however, is. This is usually at 30% to 40% of the full tree height from the butt. In a common case, the C.G. of an 80' tree could be located some 30 feet above the base of the tree. A carrier holding such a tree in a vertical position and travelling over uneven terrain would need to be large enough and heavy enough to absorb the overturning moments created by the acceleration and deceleration of the tree as it pitches randomly with the pitching of the carder.
In my experience a 25,000# carrier is acceptably stable for felling and transporting trees in a vertical position to a maximum single tree size of 20" diameter and 80' height and weighing 2,500#.
The purpose of this invention is to stabilize the tree loads against pitching and thus permit the use of much smaller and lighter carriers than would otherwise be the case. With a fully effective stabilizing means the carrier would only be required to carry an additional 2,500# directly at the felling head position. Those skilled in the art will readily see that this will permit a dramatic reduction in the size and weight of the carrier required to harvest the aforementioned tree and a commensurate improvement in the harvesting economics.
While the use of such devices is stressed as a benefit to small carriers, their utility in stabilizing any elongated object to be moved with its long axis vertically oriented will be readily seen.